Overview of Ulnar Nerve Block Techniques
An ultrasound can guide a type of procedure called an ulnar nerve block, which is used to numb the pinky finger and half of the ring finger on your hand. This is commonly used in surgeries that focus on the area that the ulnar nerve affects. It often works on its own, but sometimes it is combined with other nerve blocks for the whole hand, or used as a backup when the numbing of the brachial plexus (a network of nerves that send signals from your spinal cord to your shoulder, arm, and hand) isn’t enough.
Moreover, an ulnar nerve block can be used instead of putting the patient to sleep for painful procedures like resetting a broken bone, and as an additional method for controlling acute pain caused by burns. For patients with multiple cuts needing stitches, this type of method can be used to limit the total amount of local anesthesia (numbing medicine), while still numbing the area where the procedure will be performed.
Anatomy and Physiology of Ulnar Nerve Block Techniques
The ulnar nerve is a nerve in your arm that branches off from the group of nerves in your shoulder area called the brachial plexus. It sits near the bone in your upper arm called the humerus. As it moves down your arm, it goes into a narrow channel called the cubital tunnel, which is near your elbow. It then continues down to your forearm and to the small finger and half of the ring finger.
The ulnar nerve can be temporarily numbed or blocked at different points along the arm for pain relief during some medical procedures. However, certain methods and places for doing this block are more effective and safer according to the research.
In the past, two main methods for blocking the ulnar nerve have been suggested: the volar approach and the ulnar approach.
In the volar approach, the block is done in the lower part of your forearm, close to the wrist. The needle for the nerve block is placed just to the side of one of the forearm muscles and just above the wrist. However, this method has had some problems with the needle accidentally going into a blood vessel or the anesthetic being put in the wrong place in up to half of the cases!
The ulnar approach is a bit different. The needle is put into a different location near the wrist. Studies have not found any cases where the anesthesia goes into a blood vessel or where it is accidentally placed in the wrong location with this method, making it safer than the volar approach.
It’s not a good idea to block the ulnar nerve at the level of the elbow. This can lead to nerve damage and ongoing strange sensations or numbness.
Why do People Need Ulnar Nerve Block Techniques
An ulnar nerve block is a type of anesthetic procedure specifically for operations that don’t need a tourniquet (a device used to stop blood flow) and are intended to last less than 20 minutes. It’s often used for:
- Surgeries involving the pinky finger or the fifth long bone (called metacarpal) in the hand
- Fixing dislocated or broken fifth metacarpals
- Stitching up several cuts on the side of the hand and little finger closest to the ring finger
- Relief from pain for burns on the hand
- Providing an alternative method of pain relief or anesthesia when a brachial plexus block (another type of anesthetic procedure) didn’t work or wasn’t adequate>
- Additional blocking to a median nerve block (yet another type of anesthetic procedure) for surgeries involving the ring finger or for incomplete blocking due to connections between the nerves
When a Person Should Avoid Ulnar Nerve Block Techniques
There are several reasons why a nerve block, which is a procedure to numb a specific area, may not be a good option:
First, the patient may simply not want the procedure.
Second, if there is a skin infection, also known as cellulitis, or a pocket of pus, called an abscess, on the area where the injection should be given, then the procedure cannot be performed.
Third, if the patient is allergic to the medicine that is used to numb the area, it would not be safe to carry out the nerve block.
Fourth, if the person has had a very serious injury that might lead to a condition called ‘acute compartment syndrome’ (when pressure within the muscles builds to dangerous levels), it might not be advisable to do the procedure, though this is a debated point.
Lastly, if the patient has already been given a lot of local anesthetics and there is a risk of them getting a condition known as ‘local anesthetic systemic toxicity’ (which can cause serious problems like seizures and heart problems), the nerve block might not be safe.
Equipment used for Ulnar Nerve Block Techniques
For a procedure that uses ultrasound guidance to numb the ulnar nerve, here’s what’s needed:
* Local anesthetic: Typically, this is either 3 to 5mL of bupivacaine 0.5% or ropivacaine 0.5% for extended relief or 3 to 5mL of lidocaine 2% or mepivacaine 1.5% for shorter periods of relief. These drugs are commonly used to numb specific areas of your body.
* Ultrasound machine with a high-frequency linear probe: An ultrasound machine uses sound waves to create images of the body’s interior. This one requires a ‘probe’ – the handheld device that is run over your skin – with a frequency greater than 8 MHz. This helps the doctor visualize the ulnar nerve and ensure the anesthetic is delivered correctly.
* Sterile gel: This gel is applied to the skin before using the ultrasound probe. It prevents air gaps, which can distort the ultrasound images.
* Short bevel block needle: This is a type of needle with a slanted tip and is used to inject the anesthesia.
* 10mL syringe: This tool is used to measure and deliver the local anesthetic.
* Skin cleansing agents such as a povidone-iodine solution or chlorhexidine 2%: These solutions are antibacterials used to clean your skin before the procedure to prevent infection.
Who is needed to perform Ulnar Nerve Block Techniques?
Medical professionals who are skilled in using ultrasound for regional anesthesia are part of the team. These specialists use an ultrasound scanner to see exactly where to inject the anesthetic (a medicine to numb your body part), making the procedure safer and more effective. The team also includes support staff who can give you emergency medicine if it’s needed during the procedure. Everyone on the team works together to ensure your safety and comfort.
Preparing for Ulnar Nerve Block Techniques
Before a medical procedure, doctors will ask the patient’s permission, a process known as informed consent. The patient’s position during the procedure is important. If the procedure is on an arm, the patient will need to make the front of the arm (volar aspect) easily accessible. This can either be achieved by resting the arm and hand flat with the palm facing up or having the arm bent halfway at the elbow with the palm facing downward and resting against a pile of towels. The latter helps the doctor to keep still on top of the towels while using the ultrasound device.
Next, the doctor will clean the area where the procedure will take place with povidone-iodine or chlorhexidine 2%, both of which are commonly used antiseptics that kill bacteria and other microorganisms. To make sure the ultrasound device is also clean, a sterile protective cover is put on it, and a sterile gel is applied.
The doctor will then prepare a syringe with a local anesthetic, which is a drug that blocks the feeling of pain in a particular area. Doctors keep an eye on the patient during this time and are ready for any potential severe reactions to the local anesthetic with a drug called intralipid 20%, which can limit the harmful effects of the anesthetic if it accidentally gets into the bloodstream.
How is Ulnar Nerve Block Techniques performed
The procedure is carried out as follows:
1. Place the ultrasound scanning device across the inside of your forearm, just a little below the bony bump on the bend of the arm. This helps us see what’s going on beneath the skin.
2. The ulnar nerve looks like a white structure with a honeycomb-like pattern sitting below a muscle in your forearm called the flexor carpi ulnaris. This is the nerve we will be working with.
3. We will then track this nerve down the arm, about 1.2 to 1.6 inches away from the spot where it passes the inner part of the elbow.
4. We will insert a needle from the outer edge (thumb side) to the inner edge (little finger side) of your forearm. We have to make sure that we can see the needle tip at all times during this step.
5. We then push the needle just underneath the ulnar nerve.
6. To make sure that the needle is not inside a blood vessel, we draw back on the plunger of the needle. If we don’t see any blood in the needle, we’re good to go on.
7. We inject a small amount (about a teaspoon) of a numbing medicine around the nerve, moving the needle if needed.
8. We repeat the previous two steps until we have distributed enough numbing medicine around the nerve.
It’s very important to avoid injecting straight into the nerve. If it looks like the needle tip is inside the nerve, or if it hurts a lot when injecting the medicine, we will immediately stop and pull the needle out slightly. Then adjust before trying again.
Possible Complications of Ulnar Nerve Block Techniques
Complications from a medical procedure could include:
* An infection, which is when harmful bacteria or viruses enter the body and cause illness.
* Bleeding at the site where the doctor inserted a needle or other medical tool.
* An intramuscular hematoma, which is a large bruise or collection of blood within a muscle.
* A vascular puncture, which is an injury to a blood vessel caused by a needle or other sharp object.
* A vascular injection, which is when medicine or other substances are accidentally injected into a blood vessel instead of a muscle or other intended area.
* A nerve injury that could involve neuropraxia (temporary loss of nerve function) or neurolysis (loss of nerve function due to damage).
* Local anesthetic systemic toxicity (LAST), which is a serious reaction to too much local anesthesia. This can cause symptoms such as dizziness, seizures, or even heart problems.
* An allergic reaction to a local anesthetic, which could cause symptoms like hives, itching, or difficulty breathing.
What Else Should I Know About Ulnar Nerve Block Techniques?
Ultrasound technology has greatly improved the effectiveness and safety of anesthesia methods, specifically those used during regional procedures. Anesthesia guided by ultrasound often produces better results, needs less anesthetic, and has lesser risk of complications compared to traditional ‘blind’ methods or those involving a nerve stimulator. This technology allows for an ulnar nerve block – a type of anesthesia – to be performed easily and quickly in different settings.
An ulnar nerve block is a particularly good choice for surgeries involving the hand’s ulnar side, the little finger, or the fifth metacarpal bone (which is usually the case in a ‘Boxer’s’ fracture). It’s worth noting that ulnar nerve block might offer better anesthesia than a method called ‘hematoma block’.
However, sometimes blocking the ulnar or median nerve in the forearm might not provide complete surgical anesthesia, which is probably because of neural anastomoses. Neural anastomoses are complicated networks formed due to the connection between nerves, and they can vary greatly. The common anastomoses between the median and ulnar nerves have been classified into the Martin-Gruber, Marinacci, Rich-Cannieu, Kaplan, and Berrettini anastomoses. The crucial thing is to know that these anastomoses may exist, not necessarily their details.
If an ulnar nerve block is not wholly successful, a median nerve block should be considered to counter the anastomoses, and vice versa. In situations where the anastomoses are closer to the body, meaning ‘proximal’, the nerve block may need to be applied above the elbow.